New pharmacological and morphologicalo evidence continues to be supportive of our hypothesis that Ch + -Ca ++ -stimulated neurosecretion is mediated by the outward transport of NE in vesicles fused or attached to the plasmalemma. Various chemical compounds, which can be grouped into various classes on the basis of their biochemical effects, and are know to inhibit the Mg ++ -ATP stimulated uptake of NE by isolated synaptic vesicles, all prevent or block the ATP induced inhibition of Ch + -Ca ++ stimulated neurosecretion. These compounds include Li + and reserpine, which block the vesicle pump, dicyclohexylcarbodiimide, inhibitor of Mg ++ -ATPase which establishes proton gradients and 2,4-dinitrophenol, which dissipates stored energy. Electronmicroscopy has shown vesicles in an apparent secretory relationship with the plasmalemma. The contents of vesicles at the end of an invagination of the plasmalemma appears to be separated from the extracellular fluid by a partition. Characteristic changes in the morphology of the dense core are apparent.